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Query: EC:2.1.1.37 (DNA methyltransferase)
 4,983 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The adsorption of 23 new lambdoid bacteriophages to 547 strains which isolated from natural population of Enterobacteriaceae was studied. The frequency of positive combinations of phage-bacterium with adsorption is not more than 2%. A study of possible causes of limited growth of lambdoid phages in the bacterial strains revealed that neither homoimmune prophage nor prophage P2 are single factors of the growth limitation. It is found that in natural populations a selection of bacterial strains with the least limitation of phage takes place. Three cases of killing bacteria after infection with high multiplicity are found. The reason of the killing effect is manifestation of some functions by infecting phages. A new restriction-modification system is found which differs from restriction-modification system A, B, K, 15, P1, EcoRI, EcoRII. The most of strains, which adsorb phages but do not support their growth, are supposed to possess several mechanisms of restriction. Thus, the search of new restriction system in Escherichia coli is worthwhile.
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PMID:[Discovery of a new type of restriction and modification in a group of intestinal bacteria]. 33 89

Site-specific genetic recombinations promoted in vivo by the EcoRI endonuclease has been demonstrated by using constructed hybrid plasmids in which the chloramphenicol resistance gene was inactivated by insertion of DNA fragments at an EcoRI site within the gene. Such recombination can involve either the joining of intracellularly generated cohesive termini of the same DNA fragment or intermolecular ligation of different DNA fragments. DNA cleavage and ligation in vivo are precise: recombinant DNA molecules show functional continuity of the gene sequence cleaved by the enzyme and regeneration of nucleotide recognition sites for both the EcoRI endonuclease and the EcoRI DNA methylase. In other experiments, EcoRI-generated fragments of eukaryotic DNA that had not been modified by the Escherichia coli K methylase were shown to be taken up by bacterial cells and to undergo intracellular ligation to segments of bacterial plasmid DNA.
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PMID:In vivo site-specific genetic recombination promoted by the EcoRI restriction endonuclease. 33 2

An endonuclease having EcoRI specificity is produced by bacteria containing the ColE1 plasmid. Such bacterial cells fail to express restriction or modification functions in vivo, and phage or plasmid DNA obtained from ColE1-containing cells has unmodified EcoRI sites that are cleaved in vitro by purified EcoRI endonuclease or by enzyme extracted from bacteria that carry ColE1. No EcoRI DNA methylase activity associated with ColE1 has been detected. The finding of phenotypically cryptic ColE1-dependent EcoRI endonuclease activity and the absence of any detectable EcoRI modification system in ColE1-containing cells suggest a control mechanism that appears to prevent functional expression of the ColE1-determined enzyme in vivo.
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PMID:Phenotypically cryptic EcoRI endonuclease activity specified by the ColE1 plasmid. 34 63

The genes for a Class II restriction-modification system (HhaII) from Haemophilus haemolyticus have been cloned in Escherichia coli. The vector used for cloning was plasmid pBR322 which confers resistance to tetracycline and ampicillin and contains a single endonuclease R-PstI site, (formula: see text), in the ampicillin gene. The procedure developed by Bolivar et al. (1977) was used to form DNA recombinants. H. haemolyticus DNA was cleaved with PstI endonuclease and poly(dC) extensions were added to the 3'-OH termini using terminal deoxynucleotidyl transferase. Circular pBR322 DNA was cleaved to linear molecules with PstI endonuclease and poly(dG) extensions were added to the 3'-OH termini, thus regenerating the PstI cleavage site sequences. Recombinant molecules, formed by annealing the two DNAs, were used to transfect a restriction and modification-deficient strain of E. coli (HB101 r-m-recA). Tetracycline-resistant clones were tested for acquisition of restriction phenotype (as measured by growth on plates seeded with phage lambdacI-0). A single phage-resistant clone was found. The recombinant plasmid, pD110, isolated from this clone, had acquired 3 kilobases of additional DNA which could be excised with PstI endonuclease. In addition to the restriction function, cells carrying the plasmid expressed the HhaII modification function. Both activities have been partially purified by single-stranded DNA-agarose chromatography. The cloned HhaII restriction activity yields cleavage patterns identical to HinfI. A restriction map of the cloned DNA segment is presented.
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PMID:Cloning of restriction and modification genes in E. coli: the HbaII system from Haemophilus haemolyticus. 35 Jul 14

It was shown that E. coli C, E. coli MRE 600 DNA, and also plasmid DNA of Col E1, RSF 2124 from E. coli K-12, and plasmid DNA from E. coli MRE 600 were completely resistant against restriction endonuclease R. Eco RII. Plasmid DNAs of Col E1, RSF 2124 amplificated for 4 hours in the presence of chloramphenicol are sensitive to R. Eco RII but after 16-hour amplification in the presence of chloramphenicol these DNAs acquire complete resistance against R. Eco RII. These data point to the slower rate of modification of DNA in vivo by DC-methylases of Eco RII type in comparison with DNA methylase Eco RII.
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PMID:[Sensitivity of chromosomal and plasmid E. coli DNA to restriction endonuclease Eco RII]. 36 77

DNA methylase methylating adenine with formation of 6-methylaminopurine has been identified in Shigella sonnei 1188 cells which are the natural host of DDVI phage. At the same time, in DNA of DDVI phage replicating both in Sh. sonnei 1188 cells and in Escherichia coli B cells 7-methylguanine was found as the only minor base in amounts of 0.25 and 0.27 mol per 100 mol of nucleotides, respectively. The extract of the infected cells was found to contain both kinds of DNA methylases: virus-specific guanine methylase and cellular adenine methylase. The lack of 6-methylaminopurine in DNA of this phage is explained by reversible inhibition of the cell enzyme in the infected cells. The amount of methyl groups transferred by DDVI-specific methylase on DNA does not depend on the species of the infected cells and is similar in the case of unmodified SD phage DNA and DNA of T2 phage methylated by E. coli B enzyme. Guanine methylase has been shown to be a DDVI-induced modification enzyme and to protect against restriction of B-type. It methylates double-stranded DNAs only and is inhibited by S-adenosylhomocysteine.
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PMID:Specificity and functions of guanine methylase of Shigella sonnei DDVI phage. 36 9

In Shigella sonnei cells there is a host DNA specificity system responsible for modification and restriction of DDII phage. DNA methylase from Shigella stutzeri cells is specific for adenine and catalyses the appearance of 6-'-methylaminopurine in the acceptory DNA. Methylases from Shigella sonnei cells are specific for adenine and cytosine and provide for the presence of 6'-methylaminopurine and 5'-methylcytosine in DNA. The modifying activity of these cells may be equally likely associated with both the enzymes. A simplified version of the additional methylation test has been developed for the study of enzyme specificity. The results of additional and cross methylation suggest that several adenine methylases are present in the cells of these Shigella, one of these enzymes being shared by Shigella stutzeri and Shigella sonnei. The DNA's isolated from Shigella sonnei and Shigella stutzeri cells are undermethylated and in vitro undergo additional methylation upon incubation with the appropriate enzyme.
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PMID:[System of host specificity and the DNA methylases of shigellae and their phages]. 37 52

An improved method of purification of DNA methylase from Krebs II ascites cells is reported. The enzyme sediments at 8.3 S on glycerol-gradients and a major band on SDS polyacrylamide gel electrophoresis has a molecular weight of 184 000. Aggregation occurs at low salt and this may interfere with enzymic activity. The preferred double stranded DNA substrate is that rendered partially unmethylated by an in vitro repair mechanism or by isolation from methionine starved cells. Methylation of native partially methylated DNA is favoured under conditions of low salt and high temperature; conditions which encourage 'breathing' of the DNA. Methylation of native, unmethylated DNA also involves breathing but results in formation of a salt resistant tight binding complex between the enzyme and the DNA.
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PMID:Mouse DNA methylase: methylation of native DNA. 42 61

The possibility that carcinogens may affect methylase-mediated methylation of replicating DNA was investigated. A system eminently suitable for this purpose is liver regenerating after partial hepatectomy, as one injection of dimethylnitrosamine (DMN) given during the ensuing period of increased DNA synthesis induces hepatocellular carcinoma. Methylation of DNA by DNA methylase normally occurs only in proportion to DNA synthesis. Therefore simultaneous measurements were made of synthesis (incorporation of [14C]adenine into DNA adenine, or of d[5-3H]cytidine into DNA cytosine), and of methylation (incorporation of [methyl-3H]methionine into 5-methylcytosine of DNA) in liver regenerating after partial hepatectomy. After treatment with DMN, the ratio of methylation: synthesis remained within the normal range. Methyl methanesulphonate (MMS), a compound which damages DNA in regenerating liver in a similar but not identical way to DMN and which does not induce tumors in liver even when given after partial hepatectomy, caused an increase in methylation in relation to synthesis. These experiments therefore do not support the view that altered DNA methylase activity is involved in carcinogenesis.
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PMID:Effect of a single treatment with the alkylating carcinogens dimethylnitrosamine and methyl methanesulphonate on liver regenerating after partial hepatectomy. IV. Effect on methylase-mediated methylation of DNA. 47 54

After a 10 min- or more prolonged incubation of transformed mouse fibroblasts (L.-cells) with [3H]-thymidine or [3H-methyl]-methionine and a subsequent centrifugation of cell lysates in an alkaline sucrose gradient the DNA radioactivity is detected in long (28, 33 and 45S) and short (5, 13 and 18S) fragments. An increase in cell concentration in the cultural layer results in inhibition of 5S fragments linkage rather than in inhibition of their synthesis. The blocking of the Okazaki fragment linkage may be regarded as one of the inhibitory molecular mechanisms of cell depletion. Both in the case of normal and suppressed (by 99%) replication by arabofuranosylcytosine [3H]-thymidine and [3H-5-methyl] cytosine are detected in the Okazaki fragments (5S) as well as in some discrete lower molecular weight fractions (lesser than 5S) of newly synthesized DNA. Thus, replicative methylation of DNA in the fibroblasts occurs in the replicative fork during DNA synthesis and the functioning DNA methylase is an indispensable component of the replicative complex. The methylation of Okazaki fragments is non-chaotic and has a specificity other than that of total DNA. This may be due to the multiplicity and different specificity of nuclear DNA-methylases. Thus, there exist in animal cells replicative and post-replicative methylation of DNA, which may differ in the nature of substrates and enzymes, in specificity of recognizable sequences and in their functional significanse.
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PMID:[Methylation of newly synthesized DNA in mouse fibroblast culture]. 49 87


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